Recent concern about both ecology and energy conservation has prompted interest in ultraviolet (UV) radiation curable resin systems. Wire enamelers in particular have shown great interest in the UV curable systems not only because of the potential of ecological benefits that can be derived but also because of the promise of greatly increased productivity. A UV cured wire enamel is a 100% solids, totally reactive resin that can be applied in a single pass and is cured with energy (UV) that is specific to the resin only. For comparison, a typical thermally cured wire enamel contains approximately 70% solvent which must first be boiled off before the resin can be cured and then must be incinerated to prevent ecological damage. This is costly in terms of wasted energy and large quantities of solvent which are lost and cannot be recovered. Also, thermal energy is non-specific and must heat the wire substrate before the resonant system can begin to fully cure. The enamel must also be applied in multiple passes to achieve good coatings. Thus, the advantages of the UV curable system are obvious.
One specific area of interest is that of a UV curable solderable wire enamel. Initially, it was anticipated that almost any of the commercially available vinyl monomers, suitably modified with a photosensitizer, would provide a wire enamel that would be solderable. This, however, did not prove to be true. The vinyl monomers, when photosensitized, readily polymerized through a free radical mechanism initiated by UV radiation to form films with wire enamel properties. However, these types of wire enamels do not solder even at solder pot temperatures of 400.degree.-500.degree. C. The enamel film doesn't soften and flow, but simply chars, leaving a carbonaceous deposit on the wire which prevents the solder from properly wetting the copper substrate.